The Pregnant Runner

How carrying and delivering a baby affects running.

Paula Radcliffe's postpartum 2007 ING New York City Marathon win begs the question: Is there an athletic benefit to pregnancy? Although no definitive link has been proven, the biological tools needed to build new fingers, kidneys, and quads could potentially boost a new mom's performance. During pregnancy, blood volume goes up by as much as 40 percent and resting heart rate rises by as much as 15 beats. "Pregnancy makes you hypertrained. Your body becomes very efficient at circulating oxygen," says Nadya Swedan, M.D., author of The Active Woman's Health and Fitness Handbook. "If you begin running within weeks of giving birth, you can capitalize on those gains."

And today's expecting mothers benefit from fitter pregnancies. "We went from 'Be really careful' to, in most cases, 'Go for it,'" says James Pivarnik, who directs Michigan State University's Human Energy Research Laboratory and has studied athletic women before and after childbirth.

That said, right after giving birth, Radcliffe suffered a stress fracture in her sacrum. "Your bones can get leached of calcium, which makes them susceptible to fractures," says Dr. Swedan, a rehabilitation specialist in New York City. Knee pain is also common in postpartum running mothers who are still lugging pregnancy weight. "Your joints take more stress than they're used to," says Dr. Swedan. What's more, the hormone relaxin, which causes joints and ligaments to loosen up so the hips can accommodate giving birth, doesn't depart the body until at least four months postpartum. "It makes you more prone to sprains," says Dr. Swedan.

Perhaps, though, the most crucial gain is mental, thanks to having survived the worse-than-any-workout agony of childbirth. Indeed, a study at the University of Stirling in Scotland compared the pain tolerances of 10 women who hadn't given birth with 10 who had. During normal training sessions, the mothers handled more pain. No surprise there, as any new mom knows.